A two-dimensional eddy current array–based sensing film for estimating failure modes and tracking damage growth of bolted joints

Bolted joints are the key components for enduring primary load and play a vital role in ensuring structural safety for aircrafts. But it is very difficult to analyze the strength and failure modes of bolted joints due to their complexity and nonlinear coupling factors. Therefore, it is greatly essential to estimate potential failure mode at the early age and quantitatively track the damage parameters for calculating residual life and determining structural integrity. In this article, the concept of two-dimensional eddy current array–based sensing film is proposed to estimate the failure modes by identifying the circumferential location of the damage around the bolt hole and quantitatively track the damage parameters including the damage size in the radial direction and the damage depth in the axial direction of bolt hole. Finite element simulation is utilized to study the interaction between eddy current signals and the damage, and optimize the configuration of sensing film. Simulation result shows that a noticeable difference of eddy current signals of sensing film can be clearly seen that damage is located at different circumferential location around the hole. In addition, the exciting coil with opposite current directions at the boundary of axially adjacent coils has a better capacity of differentiating the damage sizes in the radial and axial direction than that with same current directions. The experiment is conducted to demonstrate the effectiveness of the proposed sensing film for estimating fatigue modes and quantitatively tracking damage growth.